In GtkSalFrame::UpdateSettings, we need to get an unused GtkSalGraphics instance with which to update the settings. To get the graphics, we call on GtkSalFrame::GetGraphics, however the semantics of this function are such that if it can't find an unused graphics then it will return NULL to let us know.
Unfortunately, we don't do a NULL check, and just assume that it will always return a valid graphics pointer. Hence LO will crash.
Chris Sherlock committed a patch related to this issue.
It has been pushed to "master":
fdo#74931 Prevent UpdateSettings from dereferencing null pointer
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.